CMV infection in solid organ transplant (SOT) recipients strongly impacts the course of recovery and success rate of this therapy. Increased morbidity that reflects the severity of infection, which can lead to graft loss and patient death, is associated with CMV disease. Despite significant advances in antiviral regimens, SOT recipients remain at risk for developing late CMV disease, after discontinuation of antiviral prophylaxis. Alternative approaches to preventing life-threatening CMV disease are a critical priority in the management of CMV-negative recipients (R-) of SOT from a CMV-positive donor (D+), since CMV primary infection progresses to clinical disease in ~30% of D+/R-. Our long term goal is to characterize quality and quantity of primary anti- CMV response in D+/R- recipients, for developing preventive and therapeutic strategies for patients susceptible to increased risk of CMV disease. We have reported that the acquisition of T-cell lytic function and IFN-3 production in response to rising CMV viraemia is an unreliable indicator of a protective immune response, in D+/R- liver transplant (Tx) patients. In contrast, high levels of the negative immune-modulator programmed death (PD)-1 receptor on CMV-specific T-cells are predictive of CMV disease. Our Preliminary Studies indicate that in CMV symptomatic D+/R- patients there is a parallel increased production of suppressive interleukin (IL)- 10 with increased expression of PD-1. Additionally, functional CMV-specific T-cells, expressing high PD-1 levels, show a marked deficit of proliferation. The central hypothesis of this proposal is that elevated levels of inhibitory immune-signaling indicate a state of immune impairment, which precedes development of CMV disease: reversal of the immunosuppressive environment should restore protective CMV immunity. The objective of this proposal is to characterize the post-Tx kinetics of PD-1 and IL-10 expression, which will lay the ground work for a blocking strategy of these negative immuno-modulators. A cohort of 35 liver, lung and heart D+/R- patients, in which ~12 are expected to develop CMV disease, will be monitored biweekly within 6 months after Tx, for CMV disease, CMV-specific clinical parameters and activation markers, PD-1 and IL-10. Immune- monitoring of CMV-specific T-cells will include multi-parameter flow cytometry analyses following stimulation with CMV viral lysate and 6 peptide libraries, encompassing immunodominant and frequently recognized CMV antigens (pp65, IE1, IE2, US3, US32, UL99). These longitudinal data will help identify the immune status or degree of immune-dysregulation of SOT recipients with primary CMV infection. Next, the impact of anti-PD-1 and/or IL-10 antibodies in restoring the proliferative capacity of CMV-specific T-cells will be determined in patients with CMV disease. These latter results will prove informative to design a clinical trial of an antibody blockade platform, to be used in the clinical management of high risk SOT recipients, and/or to increase the efficacy of anti-CMV vaccination strategies. This R21 award will provide the rationale for antibody-based clinical trials to reduce the incidence and/or impact of CMV disease incidence in SOT recipients. PUBLIC HEALTH RELEVANCE: The proposed studies are aimed to reduce the mortality and improve the clinical management of patients that have received solid organ transplantation (SOT). Due to anti-rejection and immunosuppressive treatments, SOT recipients become highly susceptible to several pathogens, among which cytomegalovirus (CMV) is the most significant clinical infection impairing recovery. In our project, we will characterize the immune dysfunctions that lead to life-threatening CMV complications, with the purpose of formulating preventive or therapeutic strategies to revert such defects in high risk SOT patients.